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<a name="strerror"></a>
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<hr>
<a name="strerror_002c-strerror_005fl_002d_002d_002dconvert-error-number-to-string"></a>
<h3 class="section">5.27 <code>strerror</code>, <code>strerror_l</code>&mdash;convert error number to string</h3>
<a name="index-strerror"></a>
<a name="index-strerror_005fl"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;string.h&gt;
char *strerror(int <var>errnum</var>);
char *strerror_l(int <var>errnum</var>, locale_t <var>locale</var>);
char *_strerror_r(struct _reent <var>ptr</var>, int <var>errnum</var>,
    int <var>internal</var>, int *<var>error</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>strerror</code> converts the error number <var>errnum</var> into a
string.  The value of <var>errnum</var> is usually a copy of <code>errno</code>.
If <code>errnum</code> is not a known error number, the result points to an
empty string.
</p>
<p><code>strerror_l</code> is like <code>strerror</code> but creates a string in a format
as expected in locale <var>locale</var>.  If <var>locale</var> is LC_GLOBAL_LOCALE or
not a valid locale object, the behaviour is undefined.
</p>
<p>This implementation of <code>strerror</code> prints out the following strings
for each of the values defined in &lsquo;<code>errno.h</code>&rsquo;:
</p>
<dl compact="compact">
<dt><code>0</code></dt>
<dd><p>Success
</p>
</dd>
<dt><code>E2BIG</code></dt>
<dd><p>Arg list too long
</p>
</dd>
<dt><code>EACCES</code></dt>
<dd><p>Permission denied
</p>
</dd>
<dt><code>EADDRINUSE</code></dt>
<dd><p>Address already in use
</p>
</dd>
<dt><code>EADDRNOTAVAIL</code></dt>
<dd><p>Address not available
</p>
</dd>
<dt><code>EADV</code></dt>
<dd><p>Advertise error
</p>
</dd>
<dt><code>EAFNOSUPPORT</code></dt>
<dd><p>Address family not supported by protocol family
</p>
</dd>
<dt><code>EAGAIN</code></dt>
<dd><p>No more processes
</p>
</dd>
<dt><code>EALREADY</code></dt>
<dd><p>Socket already connected
</p>
</dd>
<dt><code>EBADF</code></dt>
<dd><p>Bad file number
</p>
</dd>
<dt><code>EBADMSG</code></dt>
<dd><p>Bad message
</p>
</dd>
<dt><code>EBUSY</code></dt>
<dd><p>Device or resource busy
</p>
</dd>
<dt><code>ECANCELED</code></dt>
<dd><p>Operation canceled
</p>
</dd>
<dt><code>ECHILD</code></dt>
<dd><p>No children
</p>
</dd>
<dt><code>ECOMM</code></dt>
<dd><p>Communication error
</p>
</dd>
<dt><code>ECONNABORTED</code></dt>
<dd><p>Software caused connection abort
</p>
</dd>
<dt><code>ECONNREFUSED</code></dt>
<dd><p>Connection refused
</p>
</dd>
<dt><code>ECONNRESET</code></dt>
<dd><p>Connection reset by peer
</p>
</dd>
<dt><code>EDEADLK</code></dt>
<dd><p>Deadlock
</p>
</dd>
<dt><code>EDESTADDRREQ</code></dt>
<dd><p>Destination address required
</p>
</dd>
<dt><code>EEXIST</code></dt>
<dd><p>File exists
</p>
</dd>
<dt><code>EDOM</code></dt>
<dd><p>Mathematics argument out of domain of function
</p>
</dd>
<dt><code>EFAULT</code></dt>
<dd><p>Bad address
</p>
</dd>
<dt><code>EFBIG</code></dt>
<dd><p>File too large
</p>
</dd>
<dt><code>EHOSTDOWN</code></dt>
<dd><p>Host is down
</p>
</dd>
<dt><code>EHOSTUNREACH</code></dt>
<dd><p>Host is unreachable
</p>
</dd>
<dt><code>EIDRM</code></dt>
<dd><p>Identifier removed
</p>
</dd>
<dt><code>EILSEQ</code></dt>
<dd><p>Illegal byte sequence
</p>
</dd>
<dt><code>EINPROGRESS</code></dt>
<dd><p>Connection already in progress
</p>
</dd>
<dt><code>EINTR</code></dt>
<dd><p>Interrupted system call
</p>
</dd>
<dt><code>EINVAL</code></dt>
<dd><p>Invalid argument
</p>
</dd>
<dt><code>EIO</code></dt>
<dd><p>I/O error
</p>
</dd>
<dt><code>EISCONN</code></dt>
<dd><p>Socket is already connected
</p>
</dd>
<dt><code>EISDIR</code></dt>
<dd><p>Is a directory
</p>
</dd>
<dt><code>ELIBACC</code></dt>
<dd><p>Cannot access a needed shared library
</p>
</dd>
<dt><code>ELIBBAD</code></dt>
<dd><p>Accessing a corrupted shared library
</p>
</dd>
<dt><code>ELIBEXEC</code></dt>
<dd><p>Cannot exec a shared library directly
</p>
</dd>
<dt><code>ELIBMAX</code></dt>
<dd><p>Attempting to link in more shared libraries than system limit
</p>
</dd>
<dt><code>ELIBSCN</code></dt>
<dd><p><code>.lib</code> section in a.out corrupted
</p>
</dd>
<dt><code>EMFILE</code></dt>
<dd><p>File descriptor value too large
</p>
</dd>
<dt><code>EMLINK</code></dt>
<dd><p>Too many links
</p>
</dd>
<dt><code>EMSGSIZE</code></dt>
<dd><p>Message too long
</p>
</dd>
<dt><code>EMULTIHOP</code></dt>
<dd><p>Multihop attempted
</p>
</dd>
<dt><code>ENAMETOOLONG</code></dt>
<dd><p>File or path name too long
</p>
</dd>
<dt><code>ENETDOWN</code></dt>
<dd><p>Network interface is not configured
</p>
</dd>
<dt><code>ENETRESET</code></dt>
<dd><p>Connection aborted by network
</p>
</dd>
<dt><code>ENETUNREACH</code></dt>
<dd><p>Network is unreachable
</p>
</dd>
<dt><code>ENFILE</code></dt>
<dd><p>Too many open files in system
</p>
</dd>
<dt><code>ENOBUFS</code></dt>
<dd><p>No buffer space available
</p>
</dd>
<dt><code>ENODATA</code></dt>
<dd><p>No data
</p>
</dd>
<dt><code>ENODEV</code></dt>
<dd><p>No such device
</p>
</dd>
<dt><code>ENOENT</code></dt>
<dd><p>No such file or directory
</p>
</dd>
<dt><code>ENOEXEC</code></dt>
<dd><p>Exec format error
</p>
</dd>
<dt><code>ENOLCK</code></dt>
<dd><p>No lock
</p>
</dd>
<dt><code>ENOLINK</code></dt>
<dd><p>Virtual circuit is gone
</p>
</dd>
<dt><code>ENOMEM</code></dt>
<dd><p>Not enough space
</p>
</dd>
<dt><code>ENOMSG</code></dt>
<dd><p>No message of desired type
</p>
</dd>
<dt><code>ENONET</code></dt>
<dd><p>Machine is not on the network
</p>
</dd>
<dt><code>ENOPKG</code></dt>
<dd><p>No package
</p>
</dd>
<dt><code>ENOPROTOOPT</code></dt>
<dd><p>Protocol not available
</p>
</dd>
<dt><code>ENOSPC</code></dt>
<dd><p>No space left on device
</p>
</dd>
<dt><code>ENOSR</code></dt>
<dd><p>No stream resources
</p>
</dd>
<dt><code>ENOSTR</code></dt>
<dd><p>Not a stream
</p>
</dd>
<dt><code>ENOSYS</code></dt>
<dd><p>Function not implemented
</p>
</dd>
<dt><code>ENOTBLK</code></dt>
<dd><p>Block device required
</p>
</dd>
<dt><code>ENOTCONN</code></dt>
<dd><p>Socket is not connected
</p>
</dd>
<dt><code>ENOTDIR</code></dt>
<dd><p>Not a directory
</p>
</dd>
<dt><code>ENOTEMPTY</code></dt>
<dd><p>Directory not empty
</p>
</dd>
<dt><code>ENOTRECOVERABLE</code></dt>
<dd><p>State not recoverable
</p>
</dd>
<dt><code>ENOTSOCK</code></dt>
<dd><p>Socket operation on non-socket
</p>
</dd>
<dt><code>ENOTSUP</code></dt>
<dd><p>Not supported
</p>
</dd>
<dt><code>ENOTTY</code></dt>
<dd><p>Not a character device
</p>
</dd>
<dt><code>ENXIO</code></dt>
<dd><p>No such device or address
</p>
</dd>
<dt><code>EOPNOTSUPP</code></dt>
<dd><p>Operation not supported on socket
</p>
</dd>
<dt><code>EOVERFLOW</code></dt>
<dd><p>Value too large for defined data type
</p>
</dd>
<dt><code>EOWNERDEAD</code></dt>
<dd><p>Previous owner died
</p>
</dd>
<dt><code>EPERM</code></dt>
<dd><p>Not owner
</p>
</dd>
<dt><code>EPIPE</code></dt>
<dd><p>Broken pipe
</p>
</dd>
<dt><code>EPROTO</code></dt>
<dd><p>Protocol error
</p>
</dd>
<dt><code>EPROTOTYPE</code></dt>
<dd><p>Protocol wrong type for socket
</p>
</dd>
<dt><code>EPROTONOSUPPORT</code></dt>
<dd><p>Unknown protocol
</p>
</dd>
<dt><code>ERANGE</code></dt>
<dd><p>Result too large
</p>
</dd>
<dt><code>EREMOTE</code></dt>
<dd><p>Resource is remote
</p>
</dd>
<dt><code>EROFS</code></dt>
<dd><p>Read-only file system
</p>
</dd>
<dt><code>ESHUTDOWN</code></dt>
<dd><p>Can&rsquo;t send after socket shutdown
</p>
</dd>
<dt><code>ESOCKTNOSUPPORT</code></dt>
<dd><p>Socket type not supported
</p>
</dd>
<dt><code>ESPIPE</code></dt>
<dd><p>Illegal seek
</p>
</dd>
<dt><code>ESRCH</code></dt>
<dd><p>No such process
</p>
</dd>
<dt><code>ESRMNT</code></dt>
<dd><p>Srmount error
</p>
</dd>
<dt><code>ESTRPIPE</code></dt>
<dd><p>Strings pipe error
</p>
</dd>
<dt><code>ETIME</code></dt>
<dd><p>Stream ioctl timeout
</p>
</dd>
<dt><code>ETIMEDOUT</code></dt>
<dd><p>Connection timed out
</p>
</dd>
<dt><code>ETXTBSY</code></dt>
<dd><p>Text file busy
</p>
</dd>
<dt><code>EWOULDBLOCK</code></dt>
<dd><p>Operation would block (usually same as EAGAIN)
</p>
</dd>
<dt><code>EXDEV</code></dt>
<dd><p>Cross-device link
</p>
</dd>
</dl>


<p><code>_strerror_r</code> is a reentrant version of the above.
</p>
<br>
<p><strong>Returns</strong><br>
This function returns a pointer to a string.  Your application must
not modify that string.
</p>
<br>
<p><strong>Portability</strong><br>
ANSI C requires <code>strerror</code>, but does not specify the strings used
for each error number.
</p>
<p><code>strerror_l</code> is POSIX-1.2008.
</p>
<p>Although this implementation of <code>strerror</code> is reentrant (depending
on <code>_user_strerror</code>), ANSI C declares that subsequent calls to
<code>strerror</code> may overwrite the result string; therefore portable
code cannot depend on the reentrancy of this subroutine.
</p>
<p>Although this implementation of <code>strerror</code> guarantees a non-null
result with a NUL-terminator, some implementations return <code>NULL</code>
on failure.  Although POSIX allows <code>strerror</code> to set <code>errno</code>
to EINVAL on failure, this implementation does not do so (unless
you provide <code>_user_strerror</code>).
</p>
<p>POSIX recommends that unknown <var>errnum</var> result in a message
including that value, however it is not a requirement and this
implementation does not provide that information (unless you
provide <code>_user_strerror</code>).
</p>
<p>This implementation of <code>strerror</code> provides for user-defined
extensibility.  <code>errno.h</code> defines <var>__ELASTERROR</var>, which can be
used as a base for user-defined error values.  If the user supplies a
routine named <code>_user_strerror</code>, and <var>errnum</var> passed to
<code>strerror</code> does not match any of the supported values,
<code>_user_strerror</code> is called with three arguments.  The first is of
type <var>int</var>, and is the <var>errnum</var> value unknown to <code>strerror</code>.
The second is of type <var>int</var>, and matches the <var>internal</var> argument
of <code>_strerror_r</code>; this should be zero if called from <code>strerror</code>
and non-zero if called from any other function; <code>_user_strerror</code> can
use this information to satisfy the POSIX rule that no other
standardized function can overwrite a static buffer reused by
<code>strerror</code>.  The third is of type <var>int *</var>, and matches the
<var>error</var> argument of <code>_strerror_r</code>; if a non-zero value is stored
into that location (usually <var>EINVAL</var>), then <code>strerror</code> will set
<code>errno</code> to that value, and the XPG variant of <code>strerror_r</code> will
return that value instead of zero or <var>ERANGE</var>.  <code>_user_strerror</code>
returns a <var>char *</var> value; returning <var>NULL</var> implies that the user
function did not choose to handle <var>errnum</var>.  The default
<code>_user_strerror</code> returns <var>NULL</var> for all input values.  Note that
<code>_user_sterror</code> must be thread-safe, and only denote errors via the
third argument rather than modifying <code>errno</code>, if <code>strerror</code> and
<code>strerror_r</code> are are to comply with POSIX.
</p>
<p><code>strerror</code> requires no supporting OS subroutines.
</p>
<br>

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